1. Field of the Invention
This invention relates to a method and an apparatus for drying a work of glass, metal or other materials, and more particularly to a method and an apparatus for drying a wet work, for example, subsequent to a washing operation, by a high precision operation keeping work surfaces free of stains or spots.
2. Description of the Prior Art
There has thus far been known in the art the so-called hot D.I. (deionized) water bath drying as described, for example, in Japanese Laid-Open Patent Application 64-53549, in which a wet work which has undergone a washing treatment is immersed in a hot D.I. water bath of a predetermined temperature and then pulled out of the bath to let the work dry by its own heat. This hot D.I. water bath drying which does not resort to any organic solvent has been drawing much attention as an optimum technology for drying various articles since it is free of the problem of environmental contamination and simple in terms of operational facilities and maintenance.
In the hot D.I. water bath drying, however, one sometimes meet a problem that water remains on a particular part of a work which has been lifted out of a hot D.I. water bath, taking a longer drying time than other parts of the work and leaving a spot or stain on that part due to delayed drying. This problem is likely to occur particularly when drying a work of a shape which easily picks up water thereon, for example, a work with a broad upturned surface, a blind hole, a recess and so forth. A work which has been lifted out of the hot D.I. water bath gradually cools off as it is deprived of evaporation heat in the course of drying, making it difficult to dry off promptly the water droplets which remain on particular regions of the cooled work. These droplets tend to result in spots or stains unless they are evaporated promptly.
In this regard, it is known to blast hot air against a wet work to accelerate its drying. However, this method has a number of problems which bar precise drying operations, for example, irregularities in the degree of drying depending upon the direction of hot blasts and spots or stains of water droplets which are blown by hot blasts and relocated on or along dried surface of the work in the evaporating and drying phases of the operation. Besides, depending upon the shape of the work, a work surface which bears water droplets may become a dead zone relative to the hot blasts, necessitating an objectionably long drying time. There arises another problem that the work is susceptible to contamination with dust since dust in a drying chamber or from a hot air source is also blasted against the work.
Further, in the so-called vacuum drying method which is also known in the art, water pools or droplets on a work surface need to be evaporated by thermal energy of the work itself. Therefore, in a case where a work is subjected to vacuum drying in a cooled state after a washing operation, the work might be freezed by a further temperature drop or might take a considerably long time for drying. In this connection, it is conceivable to provide a heater on the vacuum drying machine as an auxiliary heating means for the work. However, there has to be provided a heating device of large scale to serve for this purpose, in addition to the difficulty of transferring heat efficiently and uniformly from the heating device to the work within a reasonably short period of time. For example, in a process where a work is successively subjected to washing and drying operations, it is almost impossible to complete the drying operation in a short time period, namely, to impart necessary thermal energy to the work to a sufficient degree within a limited time (e.g., about 5 minutes) which is allotted to the drying operation. Besides, there is another problem that the work is likely to be contaminated during the vacuum drying operation with dust coming from the heater for the work and the gaskets which are used for sealing the vacuum vessel.